ENHANCED MANAGEMENT OF ACs IN MULTI-USER EDCA TRANSMISSION MODE IN WIRELESS NETWORKS

ABSTRACT

To avoid blocking node AC queues in the degraded MU EDCA mode due to regular OFDMA transmission of data from another AC queue in resource units provided by an AP, the present invention proposes to use a dedicated HEMUEDCATimer for each AC queue, in order for them to be able to exit the degraded MU EDCA mode independently of the other AC queues. In this respect, upon successfully transmitting data stored in two or more traffic queues, in each of one or more accessed resource units provided by the AP within one or more transmission opportunities, the node sets each traffic queue transmitting in the accessed resource unit in the degraded MU EDCA mode for a predetermined degrading duration counted down by a respective timer associated with the transmitting traffic queue. Next, upon expiry of any timer, the node switches back the associated traffic queue to the conventional EDCA mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/084,479, filed on Oct. 29, 2020, which is a continuation of U.S.patent application Ser. No. 16/341,868, filed on Apr. 12, 2019, nowissued as U.S. Pat. No. 10,893,539 on Jan. 12, 2021, which is a NationalPhase application of PCT Application No. PCT/EP2017/076339, filed onOct. 16, 2017 and titled “ENHANCED MANAGEMENT OF ACs IN MULTI-USER EDCATRANSMISSION MODE IN WIRELESS NETWORKS.” This application claims thebenefit under 35 U.S.C. § 119(a)-(d) of United Kingdom PatentApplication No. GB1617880.8, filed on Oct. 21, 2016. The above citedpatent applications are incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates generally to communication networks andmore specifically to communication networks offering channel accesses tonodes through contention and providing secondary accesses to the nodesto sub-channels (or Resource Units) splitting a transmission opportunityTXOP granted to an access point, in order to transmit data.

The invention finds application in wireless communication networks, inparticular in 802.11ax networks offering, to the nodes, an access to an802.11ax composite channel and/or to OFDMA Resource Units forming forinstance an 802.11ax composite channel granted to the access point andallowing Uplink communication to be performed.

BACKGROUND OF THE INVENTION

The IEEE 802.11 MAC standard defines the way Wireless local areanetworks (WLANs) must work at the physical and medium access control(MAC) level. Typically, the 802.11 MAC (Medium Access Control) operatingmode implements the well-known Distributed Coordination Function (DCF)which relies on a contention-based mechanism based on the so-called“Carrier Sense Multiple Access with Collision Avoidance” (CSMA/CA)technique.

The 802.11 medium access protocol standard or operating mode is mainlydirected to the management of communication nodes waiting for thewireless medium to become idle so as to try to access to the wirelessmedium.

The network operating mode defined by the IEEE 802.11ac standardprovides very high throughput (VHT) by, among other means, moving fromthe 2.4 GHz band which is deemed to be highly susceptible tointerference to the 5 GHz band, thereby allowing for wider frequencycontiguous channels of 80 MHz to be used, two of which may optionally becombined to get a 160 MHz channel as operating band of the wirelessnetwork.

The 802.11ac standard also tweaks control frames such as theRequest-To-Send (RTS) and Clear-To-Send (CTS) frames to allow forcomposite channels of varying and predefined bandwidths of 20, 40 or 80MHz, the composite channels being made of one or more communicationchannels that are contiguous within the operating band. The 160 MHzcomposite channel is possible by the combination of two 80 MHz compositechannels within the 160 MHz operating band. The control frames specifythe channel width (bandwidth) for the targeted composite channel.

A composite channel therefore consists of a primary channel on which agiven node performs EDCA backoff procedure to access the medium, and ofat least one secondary channel, of for example 20 MHz each.

EDCA (Enhanced Distributed Channel Access) defines traffic categoriesand four corresponding access categories that make it possible to handledifferently high-priority traffic compared to low-priority traffic.

Implementation of EDCA in the nodes can be made using a plurality oftraffic queues (known as “Access Categories”) for serving data trafficat different priorities, each traffic queue being associated with arespective queue backoff value. The queue backoff value is computed fromrespective queue contention parameters, e.g. EDCA parameters, and isused to contend for access to a communication channel in order totransmit data stored in the traffic queue.

Conventional EDCA parameters include CW_(min), CW_(max) and AIFSN foreach traffic queue, wherein CW_(min) and CW_(max) are the lower andhigher boundaries of a selection range from which an EDCA contentionwindow CW is selected for a given traffic queue. AIFSN stands forArbitration Inter-Frame Space Number, and defines the number of timeslots (usually 9 μs), additional to a DIFS interval (the total definingthe AIFS period) the node must sense the medium as idle beforedecrementing the queue backoff value associated with the traffic queueconsidered.

The EDCA parameters may be defined in a beacon frame sent by a specificnode in the network to broadcast network information.

The contention windows CW and the queue backoff values are EDCAvariables.

Conventional EDCA backoff procedure consists for the node to select aqueue backoff value for a traffic queue from the respective contentionwindow CW, and then to decrement it upon sensing the medium as idleafter the AIFS period. Once the backoff value reaches zero, the node isallowed to access the medium.

The EDCA queue backoff values or counters thus play two roles. First,they drive the nodes in efficiently accessing the medium, by reducingrisks of collisions; second, they offer management of quality ofservice, QoS, by mirroring the aging of the data contained in thetraffic queue (the more aged the data, the lower the backoff value) andthus providing different priorities to the traffic queues throughdifferent values of the EDCA parameters (especially the AIFSN parameterthat delays the start of the decrementing of the EDCA queue backoffvalues).

Thanks to the EDCA backoff procedure, the node can thus access thecommunication network using contention type access mechanism based onthe queue contention parameters, typically based on the computed queuebackoff counter or value.

The primary channel is used by the communication nodes to sense whetheror not the channel is idle, and the primary channel can be extendedusing the secondary channel or channels to form a composite channel. Theprimary channel can also be used alone.

Given a tree breakdown of the operating band into elementary 20 MHzchannels, some secondary channels are named tertiary or quaternarychannels.

In 802.11ac, all the transmissions, and thus the possible compositechannels, include the primary channel. This is because the nodes performfull Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) andNetwork Allocation Vector (NAV) tracking on the primary channel only.The other channels are assigned as secondary channels, on which thenodes have only capability of CCA (clear channel assessment), i.e.detection of an idle or busy state/status of said secondary channel.

An issue with the use of composite channels as defined in the 802.11n or802.11ac (or 802.11ax) is that the nodes compliant with a use ofcomposite channels (i.e. 802.11n and 802.11ac-compliant nodes or “HTnodes” standing for High Throughput nodes) have to co-exist with legacynodes not able to use composite channels but relying only onconventional 20 MHz channels (i.e. non-HT nodes compliant only with forinstance 802.11a/b/g) exist within the same wireless network, and thushave to share the same 20 MHz channels.

To cope with this issue, the 802.11n and 802.11ac and 802.11ax standardsprovide the possibility to duplicate control frames (e.g. RTS/CTS orCTS-to-Self or ACK frames to acknowledge correct or erroneous receptionof the sent data) over each 20 MHz channel in an 802.11a legacy format(called as “non-HT”) to establish a protection of the requested TXOPover the whole composite channel.

This is for any legacy 802.11a node that uses any of the 20 MHz channelinvolved in the composite channel to be aware of on-going communicationson the 20 MHz channel. As a result, the legacy node is prevented frominitiating a new transmission until the end of the current compositechannel TXOP granted to an 802.11 n/ac/ax node.

As originally proposed by 802.11n, a duplication of conventional 802.11aor “non-HT” transmission is provided to allow the two identical 20 MHznon-HT control frames to be sent simultaneously on both the primary andsecondary channels forming the used composite channel.

This approach has been widened for 802.11ac to allow duplication overthe channels forming an 80 MHz or 160 MHz composite channel. In theremainder of the present document, the “duplicated non-HT frame” or“duplicated non-HT control frame” or “duplicated control frame” meansthat the node device duplicates the conventional or “non-HT”transmission of a given control frame over secondary 20 MHz channel(s)of the (40 MHz, 80 MHz or 160 MHz) operating band.

In practice, to request a composite channel (equal to or greater than 40MHz) for a new TXOP, an 802.11n/ac node performs an EDCA backoffprocedure in the primary 20 MHz channel as mentioned above. In parallel,it performs a channel sensing mechanism, such as aClear-Channel-Assessment (CCA) signal detection, on the secondarychannels to detect the secondary channel or channels that are idle(channel state/status is “idle”) during a PIFS interval before the startof the new TXOP (i.e. before any queue backoff counter expires).

More recently, Institute of Electrical and Electronics Engineers (IEEE)officially approved the 802.11ax task group, as the successor of802.11ac. The primary goal of the 802.11ax task group consists inseeking for an improvement in data speed to wireless communicatingdevices used in dense deployment scenarios.

Recent developments in the 802.11ax standard sought to optimize usage ofthe composite channel by multiple nodes in a wireless network having anaccess point (AP). Indeed, typical contents have important amount ofdata, for instance related to high-definition audio-visual real-time andinteractive content. Furthermore, it is well-known that the performanceof the CSMA/CA protocol used in the IEEE 802.11 standard deterioratesrapidly as the number of nodes and the amount of traffic increase, i.e.in dense WLAN scenarios.

In this context, multi-user (MU) transmission has been considered toallow multiple simultaneous transmissions to/from different users inboth downlink (DL) and uplink (UL) directions from/to the AP and duringa transmission opportunity granted to the AP. In the uplink, multi-usertransmissions can be used to mitigate the collision probability byallowing multiple non-AP stations or nodes to simultaneously transmit.

To actually perform such multi-user transmission, it has been proposedto split a granted communication channel into sub-channels, alsoreferred to as resource units (RUs), that are shared in the frequencydomain by multiple users (non-AP stations/nodes), based for instance onOrthogonal Frequency Division Multiple Access (OFDMA) technique. Each RUmay be defined by a number of tones, the 80 MHz channel containing up to996 usable tones.

OFDMA is a multi-user variation of OFDM which has emerged as a new keytechnology to improve efficiency in advanced infrastructure-basedwireless networks. It combines OFDM on the physical layer with FrequencyDivision Multiple Access (FDMA) on the MAC layer, allowing differentsubcarriers to be assigned to different stations/nodes in order toincrease concurrency. Adjacent sub-carriers often experience similarchannel conditions and are thus grouped to sub-channels: an OFDMAsub-channel or RU is thus a set of sub-carriers.

As currently envisaged, the granularity of such OFDMA sub-channels isfiner than the original 20 MHz channel band. Typically, a 2 MHz or 5 MHzsub-channel may be contemplated as a minimal width, therefore definingfor instance 9 sub-channels or resource units within a single 20 MHzchannel.

The multi-user feature of OFDMA allows the AP to assign or offerdifferent RUs to different non-AP stations/nodes in order to increasecompetition. This may help to reduce contention and collisions inside802.11 networks.

Contrary to downlink OFDMA wherein the AP can directly send multipledata to multiple stations (supported by specific indications inside thePLCP header), a trigger mechanism has been adopted for the AP to triggermulti-user uplink (MU UL) OFDMA communications from various nodes.

To support multi-user uplink, i.e. uplink transmission to the 802.11axaccess point (AP) during a pre-empted TXOP, the 802.11ax AP has toprovide signalling information for the legacy nodes (non-802.11ax nodes)to set their NAV and for the 802.11ax nodes to determine the allocationof the resource units RUs provided by the AP.

The 802.11ax standard defines a trigger frame (TF) that is sent by theAP to the 802.11ax nodes to trigger Multi-User uplink communications.

The document IEEE 802.11-15/0365 proposes that a ‘Trigger’ frame (TF) issent by the AP to solicit the transmission of uplink (UL) Multi-User(OFDMA) PPDU from multiple nodes. The TF defines the resource units asprovided by the AP to the nodes. In response, the nodes transmit UL MU(OFDMA) PPDU as immediate responses to the Trigger frame. Alltransmitters can send data at the same time, but using disjoint sets ofRUs (i.e. of frequencies in the OFDMA scheme), resulting intransmissions with less interference.

The bandwidth or width of the targeted composite channel is signalled inthe TF frame, meaning that the 20, 40, 80 or 160 MHz value is added. TheTF frame is sent over the primary 20 MHz channel and duplicated(replicated) on each other 20 MHz channels forming the targetedcomposite channel, if appropriate. As described above for theduplication of control frames, it is expected that every nearby legacynode (non-HT or 802.11ac nodes) receiving the TF on its primary channel,then sets its NAV to the value specified in the TF. This prevents theselegacy nodes from accessing the channels of the targeted compositechannel during the TXOP.

A resource unit RU can be reserved for a specific node, in which casethe AP indicates, in the TF, the node to which the RU is reserved. SuchRU is called Scheduled RU. The indicated node does not need to performcontention on accessing a scheduled RU reserved to it.

The type of data the node is allowed to transmit in the Scheduled RU maybe specified by the AP in the TF. For instance, the TF includes a 2-bit“Preferred AC” field in which the AP indicates one of the four EDCAtraffic queues. On the other hand, the AP may let the Scheduled RU beopened to any type of data. To activate or not the “Preferred AC”, theTF includes another 1-bit field, namely “AC Preference Level”.

In order to better improve the efficiency of the system with regards toun-managed traffic to the AP (for example, uplink management frames fromassociated nodes, unassociated nodes intending to reach an AP, or simplyunmanaged data traffic), resource units may be proposed by the AP to the802.11ax nodes through contention-based access. In other words, theresource unit RU can be randomly accessed by more than one node (of thegroup of nodes registered with the AP). Such RU is called Random RU andis indicated as such in the TF. Random RUs may serve as a basis forcontention between nodes willing to access the communication medium forsending data.

An exemplary random resource selection procedure is defined in documentIEEE 802.11-15/1105. According to this procedure, each 802.11ax nodemaintains a dedicated backoff engine, referred below to as OFDMA or RU(for resource unit) backoff engine, using RU contention parameters,including an RU backoff value, to contend for access to one of therandom RUs. Once its OFDMA or RU backoff value reaches zero (it is forinstance decremented at each new TF-R frame by the number of random RUsdefined therein), a node becomes eligible for RU access and thusrandomly selects one RU from among all the random RUs defined in thereceived trigger frame. It then uses the selected RU to transmit data ofat least one of the traffic queues.

As readily apparent from the above, the Multi User Uplink medium accessscheme (or OFDMA or RU access scheme) allows the number of collisionsgenerated by simultaneous medium access attempts to be reduced, whilealso reducing the overhead due to the medium access since the mediumaccess cost is shared between several nodes. The OFDMA or RU accessscheme thus appears to be quite more efficient (with regards of themedium usage) than the conventional EDCA contention-based medium accessscheme (in the context of a high density 802.11 cell).

Although the OFDMA or RU access scheme seems more efficient, the EDCAaccess scheme must also survive and thus coexist with the OFDMA or RUaccess scheme.

This is mainly due to the existence of legacy 802.11 nodes which muststill have the opportunity to access the medium, while they are notaware of the OFDMA or RU access scheme. And the global fairness aboutthe medium access must be ensured.

This is also all the more necessary that the 802.11ax nodes should alsohave the opportunity to gain access to the medium through conventionalEDCA contention-based medium access, for instance to send data toanother node (i.e. for traffic different from uplink traffic to the AP).

So the two medium access schemes, EDCA and OFDMA/RU access schemes, haveto coexist.

This coexistence has downsides.

For instance, 802.11ax nodes and legacy nodes have the same mediumaccess probability using the EDCA access scheme. However, the 802.11axnodes have additional medium access opportunities using the MU Uplink orOFDMA or RU access scheme.

It results that access to the medium is not fully fair between the802.11ax nodes and the legacy nodes.

To restore some fairness between the nodes, solutions have been proposedto modify, upon successfully transmitting data over an accessed resourceunit (i.e. through UL OFDMA transmission), a current value of at leastone queue contention parameter into a penalized or degraded value, toreduce a probability for the node to access a communication channelthrough (EDCA) contention. For instance, the penalized or degraded valueis more restrictive than the original (or legacy) value.

For instance, document IEEE 802.11-16/1180 entitled “Proposed textchanges for MU EDCA parameters” proposes that, upon successfully (MU ULOFDMA) transmitting data in a resource unit, RU, reserved by the AP, anode is set in a MU EDCA mode, for a predetermined duration counted downby a timer (noted HEMUEDCATimer below, standing for High EfficiencyMulti-User EDCA Timer), in which the EDCA parameters are set to values,referred to as MU EDCA parameters values or MU values, different fromlegacy values used in a legacy EDCA mode. The MU parameter values areset to more restrictive values than the legacy values: more restrictivevalues for EDCA parameters means that a probability for a node to accessthe communication channel through EDCA access scheme using the MU valuesis reduced relatively to an access using the legacy values.

In other words, as soon as the node transmits some data from one or moretraffic queues using a scheduled RU assigned to the node by the AP, thenode shall modify the EDCA parameters associated with the transmittingtraffic queue(s) (here below “degraded”, “penalized” or “blocked”traffic queue(s)), with some special more restrictive (“MU” or“degraded”) values that may be provided by the AP in a dedicatedInformation Element of a beacon frame, which also includes the value tobe used by the nodes for their HEMUEDCATimer.

One may thus note that the AP sends, to the nodes, the more restrictivevalues to drive the node in modifying current values of their EDCAparameters into the MU values upon the node successfully transmittingdata over the accessed resource unit. This is also to reduce aprobability for the node to access the communication channel throughEDCA access scheme.

In addition, the AP may determine the more restrictive values based on ahistory of data received from the nodes (e.g. through RUs).

The disclosed approach suggests increasing only the value of AIFSN foreach transmitting traffic queue, while keeping CW_(min), and CW_(max)unchanged. As the corresponding AIFS period increases, the traffic queuein the MU EDCA mode is prevented (or at least substantially delayed)from having its queue backoff value or counter been decremented uponsensing the medium free, in particular in high density environment inwhich the medium does not remain free for a long time. New accesses tothe medium using EDCA access scheme are statistically substantiallyreduced, or even no longer possible.

Upon switching into the MU EDCA mode, the node starts its HEMUEDCATimercountdown. The HEMUEDCATimer is reinitialized each time the nodesuccessfully (MU UL OFDMA) transmits data in a new reserved RU. Theinitializing value of HEMUEDCATimer is suggested to be high (e.g. tensof milliseconds) in order to encompass several new opportunities for MUUL transmissions.

When the HEMUEDCATimer lapses, the traffic queues in MU EDCA mode areswitched back to the legacy EDCA mode with legacy EDCA parameters,thereby exiting the queues from the MU EDCA mode.

Thus, this mechanism of double operating modes, conventional EDCA modeand MU EDCA mode, promotes the usage of the MU UL mechanism by reducingthe probability of a MU UL transmitting node to gain access to themedium using the EDCA mechanism.

The HEMUEDCATimer mechanism of reinitializing the HEMUEDCATimer eachtime the node successfully transmits new data in accessed reserved RUmeans the node remains in the MU EDCA state as long as the AP provides(scheduled or random) RUs to the node.

This approach has a main drawback as explained now.

If the node transmits data from two or more traffic queues in one ormore resource units provided by the AP (for instance if a dedicatedtraffic queue becomes empty, the node selects other data to be sent froma traffic queue with higher priority), the two or more traffic queuesare turned into the MU and more restrictive EDCA mode. They are mainlyprevented from accessing the medium through EDCA access scheme, as forinstance their respective AIFSN are very restrictive.

It may happen that the AP regularly provides resource units to that node(being in such situation) with an indication of a preferred trafficqueue from which data are to be selected.

As long as this polling with preferred traffic queue continues, the nodeempties the corresponding traffic queue upon accessing the providedresource units, while keeping all the two or more traffic queues in theMU EDCA mode. It means the other traffic queue or queues remain lockedin the MU and more restrictive EDCA mode, and cannot be purged byaccessing the medium.

The QoS in the network is thus severely deteriorated.

SUMMARY OF INVENTION

The present invention seeks to overcome the foregoing limitations. Inparticular, it seeks to overcome the loss of QoS handling resulting fromthe introduction of the MU UL OFDMA transmissions.

The inventors have noticed the locking of the other traffic queues in aMU contention mode, such as the above MU EDCA mode, results from havingthe HEMUEDCATimer being reinitialized each time data from the same andpreferred traffic queue are (regularly) transmitted in resource units.The unicity of the HEMUEDCATimer to simultaneously manage all thetraffic queues in the MU contention mode is thus substantiallydetrimental to QoS.

The invention thus intends to restore some QoS by breaking the unicityof the HEMUEDCATimer.

In this context, the present invention proposes a communication methodin a communication network comprising a plurality of nodes, at least onenode comprising a plurality of traffic queues for serving data trafficat different priorities, each traffic queue being associated with arespective queue backoff value computed from respective queue contentionparameters having legacy values in a legacy contention mode and used tocontend for access to a communication channel in order to transmit datastored in the traffic queue;

the method comprising, at the node:

transmitting data stored in two or more traffic queues, in one or moreaccessed resource units provided by another node within one or moretransmission opportunities granted to the other node on thecommunication channel; and

upon transmitting data in each accessed resource unit, setting eachtransmitting traffic queue (i.e. transmitting in the accessed resourceunit) in a MU contention mode, different from the legacy contentionmode, for a predetermined duration counted down by a respective timerassociated with the transmitting traffic queue, wherein the respectivequeue contention parameters in the MU contention mode are set to MUvalues different from the legacy values; and

upon expiry of any timer, switching back the associated (degraded)traffic queue to the legacy contention mode in which the respectivequeue contention parameters are set back to the legacy values.

The present invention thus proposes to use a dedicated HEMUEDCATimer foreach AC queue, in order for them to be able to exit the MU contentionmode independently of the other AC queues.

Hardware or software-implemented timers can be used.

Fairness between the two contention modes is thus restored for the802.11ax nodes.

MU values different from the legacy values for a traffic queue meansthat the MU and legacy values for at least one same contention parameterdiffer one from the other, regardless of whether the MU and legacyvalues of the other contention parameters are equal or differ.

Correspondingly, the invention also regards a communication device nodein a communication network comprising a plurality of nodes, thecommunication device comprising:

a plurality of traffic queues for serving data traffic at differentpriorities, each traffic queue being associated with a respective queuebackoff value computed from respective queue contention parametershaving legacy values in a legacy contention mode and used to contend foraccess to a communication channel in order to transmit data stored inthe traffic queue;

a plurality of timers, each one associated with one of the trafficqueues; and

at least one microprocessor configured for carrying out the followingsteps:

transmitting data stored in two or more traffic queues, in one or moreaccessed resource units provided by another node within one or moretransmission opportunities granted to the other node on thecommunication channel; and

upon transmitting data in each accessed resource unit, setting eachtransmitting traffic queue in a MU contention mode, different from thelegacy contention mode, for a predetermined duration counted down by theassociated timer, wherein the respective queue contention parameters inthe MU contention mode are set to MU values different from the legacyvalues; and

upon expiry of any timer, switching back the associated (degraded)traffic queue to the legacy contention mode in which the respectivequeue contention parameters are set back to the legacy values.

The device node has the same advantages as the method defined above.

Optional features of the invention are defined in the appended claims.Some of these features are explained here below with reference to amethod, while they can be transposed into system features dedicated toany device node according to the invention.

In embodiments, the predetermined (preferably degrading) durations usedto initialize the timers associated with two respective traffic queuesare different one from the other. This configuration improves themanagement of QoS.

In other embodiments, the predetermined durations used to initialize thetimers associated with respective traffic queues are computed from acommon initializing value received from the other node and from anadjusting parameter specific to the respective traffic queue. Thecombination of the common initializing value and the adjustingparameters for the AC queues thus makes it possible to easily adjust theduration during which each AC queue should remain in the MU contentionmode. Thus, this configuration also improves the management of QoS.

In variants, the predetermined durations used to initialize the timersassociated with respective traffic queues are set to respectiveinitializing values directly received from the other node. In otherwords, the other node, such as an AP, directly drives the durationsduring which the AC queues should respectively remain in the MUcontention mode.

An efficient management of QoS can thus be achieved, in particularbecause the other node, such as an AP, may have an overall view of thenetwork (such as statistics on collisions, number of nodes, and so on.).Adjustment to give priority to such or such AC queue is thus madeeasier, and the network is consequently made more efficient.

In some embodiments, the timer associated with a respective trafficqueue is reinitialized to the corresponding predetermined duration eachtime data from the associated traffic queue is transmitted in anaccessed resource unit provided by the other node within any subsequenttransmission opportunity granted to the other node on the communicationchannel.

It means the timer for an AC queue will expires only if no data fromthis AC queue are transmitted in any resource unit provided by the othernode during the predetermined duration having initialized this timer.Otherwise, the timer is reinitialized again.

As a consequence, this traffic queue may exit the MU contention mode byrestoring the respective queue contention parameters to legacy values,only if no data from the considered AC queue are OFDMA transmittedduring the specified duration.

In embodiments, the method further comprises, at the node, contendingfor access to the communication channel using the queue contentionparameters in the MU contention mode. It means the MU contention modefollows the same contention scheme as the legacy contention mode, e.g.conventional EDCA, but with MU, preferably degraded (i.e. morerestrictive), contention parameters in order to penalize the AC queuesthat are polled by the AP to transmit in RUs.

In embodiments, the method further comprises, at the node, periodicallyreceiving a beacon frame from an access point, each beacon framebroadcasting network information about the communication network to theplurality of nodes,

wherein at least one received beacon frame includes the legacy valuesand the MU values for the queue contention parameters of the pluralityof traffic queues and at least one initializing value to initialize thetimers to the predetermined durations associated with the trafficqueues.

In embodiments, the transmitting traffic queue or queues are set in theMU contention mode only upon successfully transmitting the data in thecorresponding accessed resource unit. This configuration guaranteesfairness. Indeed, in the philosophy of contention mode switching, the MUmode should only be implemented to compensate the existence of othertransmission opportunities (here through RUs), meaning data aresuccessfully transmitted.

In some embodiments, the MU values include a degraded ArbitrationInter-Frame Space Number, AIFSN, compared to the legacy values. Thisconfiguration is simple to implement in order to directly reduce (up toa desired level) the chances of a specific traffic queue to access themedium through EDCA.

In particular, each queue backoff value may be initially selected from arespective contention window, the queue backoff value being decreased bythe node over time to access the communication channel upon reachingzero, and

the MU values of the queue contention parameters may include the samelower CW_(min) and/or higher CW_(max) boundaries, both defining aselection range from which a size of the contention window is selected,as the legacy values.

This configuration simplifies the entering into and the exiting from theMU contention mode (MU EDCA mode) since the contention window can bekept unchanged. However, variants may contemplate having differentboundaries between the legacy and MU values.

In some embodiments, the method further comprises, at the node, uponaccessing a resource unit provided by the other node within a subsequenttransmission opportunity granted to the other node:

selecting data from the traffic queues in both MU and legacy contentionmodes, based on associated current queue backoff values,

transmitting the selected data in the accessed resource unit within thenew transmission opportunity.

A fair management of QoS is thus maintained when implementing thepresent invention.

According to a specific feature, selecting data including selecting datafrom the traffic queue associated with the lowest current queue backoffvalue. EDCA-like behaviour of the AC queues is thus kept.

In alternative embodiments, the method further comprises, at the node,upon accessing a resource unit provided by the other node within asubsequent transmission opportunity granted to the other node:

selecting data from a preferred traffic queue indicated by the othernode,

transmitting the selected data in the accessed resource unit within thenew transmission opportunity.

According to a specific feature, the preferred traffic queue indicationis included in a trigger frame received from the other node, the triggerframe reserving the transmission opportunity granted to the other nodeon the communication channel and defining resource units, RUs, formingthe communication channel including the accessed resource unit.

This approach makes it possible for the other node, usually the AP, todrive the QoS management.

In some embodiments of the invention, the accessed resource unit overwhich the data are transmitted is a random resource unit, the access ofwhich being made through contention using separate RU contentionparameters (separate from the above-mentioned queue contentionparameters).

In other embodiments, the accessed resource unit over which the data aretransmitted is a scheduled resource unit, the scheduled resource beingassigned by the other node to the node.

Of course, some nodes may access scheduled RUs while other nodes maysimultaneously access random RUs, resulting in having simultaneouslyvarious nodes in the MU contention mode (for one or more AC queues).

In some embodiments, the other node is an access point of thecommunication network to which nodes register. This provisionadvantageously takes advantage of the central position of the accesspoint.

From the Access Point perspective, the present invention proposes acommunication method in a communication network comprising a pluralityof nodes and an access point, each node comprising a plurality oftraffic queues for serving data traffic at different priorities, eachtraffic queue being associated with a respective queue backoff valuecomputed from respective queue contention parameters having legacyvalues in a legacy contention mode and used to contend for access to acommunication channel in order to transmit data stored in the trafficqueue;

the method comprising, at the access point:

accessing the communication channel to send a trigger frame reserving atransmission opportunity on the communication channel and definingresource units, RUs, forming the communication channel for the nodes totransmit data to the access point

sending, to the nodes, a set of legacy values of the queue contentionparameters and a set of MU values of the queue contention parameters,different from the set of legacy values, and a set of initializingvalues of node timers associated with the traffic queues respectively,to configure each node when each of two or more traffic queues of thenode switches between a MU contention mode in which the respective queuecontention parameters are set to MU values and a legacy contention mode,to be maintained during a predetermined duration initialized based onthe associated initializing value and counted down by an associatedtimer, wherein the respective queue contention parameters in the MUcontention mode are set to respective MU values.

Correspondingly, an access point in a communication network alsocomprising a plurality of nodes, each node comprising a plurality oftraffic queues for serving data traffic at different priorities, eachtraffic queue being associated with a respective queue backoff valuecomputed from respective queue contention parameters having legacyvalues in a legacy contention mode and used to contend for access to acommunication channel in order to transmit data stored in the trafficqueue;

the access point comprising at least one microprocessor configured forcarrying out the following steps:

accessing the communication channel to send a trigger frame reserving atransmission opportunity on the communication channel and definingresource units, RUs, forming the communication channel for the nodes totransmit data to the access point

sending, to the nodes, a set of legacy values of the queue contentionparameters and a set of MU values of the queue contention parameters,different from the set of legacy values, and a set of initializingvalues of node timers associated with the traffic queues respectively,to configure each node when each of two or more traffic queues of thenode switches between a legacy contention mode in which the respectivequeue contention parameters are set to legacy values and a MU contentionmode, to be maintained during a predetermined duration initialized basedon the associated initializing value and counted down by an associatedtimer, wherein the respective queue contention parameters in the MUcontention mode are set to respective MU values.

The access point may thus efficiently control fairness in the network.Indeed, through the MU values and the values of the timers, the accesspoint may drive the nodes to adjust their EDCA access scheme under MUcontention mode, different from the conventional legacy mode.

Preferably, the legacy and MU values, as well as the timer values, canbe evaluated based on history of past transmissions from the nodes, inparticular in RUs provided by the access point (random or scheduledRUs).

Optional features of the invention are defined in the appended claims.Some of these features are explained here below with reference to amethod, while they can be transposed into system features dedicated toany device node according to the invention.

In some embodiments, the sets of legacy values and of MU values and ofinitializing values are transmitted within one or more beacon frames,periodically transmitted by the access point to broadcast networkinformation about the communication network to the plurality of nodes.

In yet other embodiments, the sets of legacy values and of MU valuesdiffer by different Arbitration Inter-Frame Space Numbers, AIFSNs.

In particular, each queue backoff value of a node may be initiallyselected from a respective contention window, the queue backoff valuebeing decreased by the node over time to access the communicationchannel upon reaching zero, and

the sets of legacy values and of MU values may include the same lowerboundaries CW_(min) and/or higher boundaries CW_(max), both definingtogether selection ranges from which sizes of the contention windowsassociated with the traffic queues are respectively selected.

Another aspect of the invention relates to a non-transitorycomputer-readable medium storing a program which, when executed by amicroprocessor or computer system in a device, causes the device toperform any method as defined above.

The non-transitory computer-readable medium may have features andadvantages that are analogous to those set out above and below inrelation to the methods and devices.

Another aspect of the invention relates to a method, substantially asherein described with reference to, and as shown in, FIG. 5 b , or FIG.11 , or FIGS. 11 and 12 , or FIGS. 11, 12 and 14 b, or FIGS. 11, 12 and14 c of the accompanying drawings.

At least parts of the methods according to the invention may be computerimplemented. Accordingly, the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit”, “module” or “system”. Furthermore,the present invention may take the form of a computer program productembodied in any tangible medium of expression having computer usableprogram code embodied in the medium.

Since the present invention can be implemented in software, the presentinvention can be embodied as computer readable code for provision to aprogrammable apparatus on any suitable carrier medium. A tangiblecarrier medium may comprise a storage medium such as a hard disk drive,a magnetic tape device or a solid state memory device and the like. Atransient carrier medium may include a signal such as an electricalsignal, an electronic signal, an optical signal, an acoustic signal, amagnetic signal or an electromagnetic signal, e.g. a microwave or RFsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent tothose skilled in the art upon examination of the drawings and detaileddescription. Embodiments of the invention will now be described, by wayof example only, and with reference to the following drawings.

FIG. 1 illustrates a typical wireless communication system in whichembodiments of the invention may be implemented;

FIGS. 2 a, 2 b illustrate the IEEE 802.11e EDCA involving accesscategories;

FIG. 2 c illustrates an example of values for the degraded EDCAparameter set.

FIG. 3 a illustrates 802.11ac mechanism for the backoff countercountdown;

FIG. 3 b illustrates an example of mapping between eight priorities oftraffic class and the four EDCA ACs.

FIG. 4 illustrates an example of 802.11ax uplink OFDMA transmissionscheme, wherein the AP issues a Trigger Frame for reserving atransmission opportunity of OFDMA sub-channels (resource units) on an 80MHz channel as known in the art;

FIG. 4 a illustrates 802.11ac channel allocation that support channelbandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;

FIG. 5 a illustrates the states of transmitting traffic queues switchedin MU EDCA mode as known in the prior art;

FIG. 5 b illustrates the states of transmitting traffic queues switchedin MU EDCA mode according to embodiments of the invention;

FIG. 6 shows a schematic representation a communication device orstation in accordance with embodiments of the present invention;

FIG. 7 shows a schematic representation of a wireless communicationdevice in accordance with embodiments of the present invention;

FIG. 8 illustrates an exemplary transmission block of a communicationnode according to embodiments of the invention;

FIG. 9 illustrates, using a flowchart, main steps performed by a MAClayer of a node, when receiving new data to transmit, in embodiments ofthe invention;

FIG. 10 illustrates, using a flowchart, steps of accessing the mediumbased on the EDCA medium access scheme, in both situations withnon-degraded EDCA parameters or with degraded EDCA parameters, accordingto embodiments of the invention;

FIG. 11 illustrates, using a flowchart, steps of accessing resourceunits based on an RU or OFDMA access scheme upon receiving a triggerframe defining RUs according to embodiments of the invention;

FIG. 12 illustrates, using a flowchart, the node management to switchback to the non-degraded mode, according to embodiments of theinvention;

FIG. 13 illustrates the structure of a trigger frame as defined in the802.11ax standard;

FIG. 14 a illustrates the structure of a standardized informationelement used to describe the parameters of the EDCA in a beacon frame;and

FIGS. 14 b and 14 c illustrate exemplary structures of a dedicatedinformation element to transmit the degraded EDCA parameter valuesaccording to embodiments of the invention, as well as the HEMUEDCATimervalue.

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limitingexemplary embodiments and by reference to the figures.

FIG. 1 illustrates a communication system in which several communicationnodes (or stations) 101-107 exchange data frames over a radiotransmission channel 100 of a wireless local area network (WLAN), underthe management of a central station, or access point (AP) 110 with whichthe nodes have registered. The radio transmission channel 100 is definedby an operating frequency band constituted by a single channel or aplurality of channels forming a composite channel.

Access to the shared radio medium to send data frames is based on theCSMA/CA technique, for sensing the carrier and avoiding collision byseparating concurrent transmissions in space and time.

Carrier sensing in CSMA/CA is performed by both physical and virtualmechanisms. Virtual carrier sensing is achieved by transmitting controlframes to reserve the medium prior to transmission of data frames.

Next, a source or transmitting node, including the AP, first attempts,through the physical mechanism, to sense a medium that has been idle forat least one DIFS (standing for DCF InterFrame Spacing) time period,before transmitting data frames.

However, if it is sensed that the shared radio medium is busy during theDIFS period, the source node continues to wait until the radio mediumbecomes idle.

To access the medium, the node starts a countdown backoff counterdesigned to expire after a number of timeslots, chosen randomly in aso-called contention window [0, CW], CW (integer). This backoffmechanism or procedure, also referred to as channel access scheme, isthe basis of the collision avoidance mechanism that defers thetransmission time for a random interval, thus reducing the probabilityof collisions on the shared channel. After the backoff time period (i.e.the backoff counter reaches zero), the source node may send data orcontrol frames if the medium is idle.

One problem of wireless data communications is that it is not possiblefor the source node to listen while sending, thus preventing the sourcenode from detecting data corruption due to channel fading orinterference or collision phenomena. A source node remains unaware ofthe corruption of the data frames sent and continues to transmit theframes unnecessarily, thus wasting access time.

The Collision Avoidance mechanism of CSMA/CA thus provides positiveacknowledgement (ACK) of the sent data frames by the receiving node ifthe frames are received with success, to notify the source node that nocorruption of the sent data frames occurred.

The ACK is transmitted at the end of reception of the data frame,immediately after a period of time called Short InterFrame Space (SIFS).

If the source node does not receive the ACK within a specified ACKtimeout or detects the transmission of a different frame on the channel,it may infer data frame loss. In that case, it generally reschedules theframe transmission according to the above-mentioned backoff procedure.

To improve the Collision Avoidance efficiency of CSMA/CA, a four-wayhandshaking mechanism is optionally implemented. One implementation isknown as the RTS/CTS exchange, defined in the 802.11 standard.

The RTS/CTS exchange consists in exchanging control frames to reservethe radio medium prior to transmitting data frames during a transmissionopportunity called TXOP in the 802.11 standard, thus protecting datatransmissions from any further collisions. The four-way CTS/RTShandshaking mechanism is well known, and thus not further describedhere. Reference is made to the standard for further details

The RTS/CTS four-way handshaking mechanism is very efficient in terms ofsystem performance, in particular with regard to large frames since itreduces the length of the messages involved in the contention process.

In detail, assuming perfect channel sensing by each communication node,collision may only occur when two (or more) frames are transmittedwithin the same time slot after a DIFS (DCF inter-frame space) or whenthe backoff counters of the two (or more) source nodes have reached zeronearly at the same time. If both source nodes use the RTS/CTS mechanism,this collision can only occur for the RTS frames. Fortunately, suchcollision is early detected by the source nodes upon not receiving a CTSresponse.

Management of quality of service (QoS) has been introduced at node levelin such wireless networks, through well-known EDCA mechanism defined inthe IEEE 802.11e standard.

Indeed, in the original DCF standard, a communication node includes onlyone transmission queue/buffer. However, since a subsequent data framecannot be transmitted until the transmission/retransmission of apreceding frame ends, the delay in transmitting/retransmitting thepreceding frame prevented the communication from having QoS.

FIGS. 2 a, and 2 b illustrate the IEEE 802.11e EDCA mechanism involvingaccess categories, in order to improve the quality of service (QoS).

The 802.11e standard relies on a coordination function, called hybridcoordination function (HCF), which has two modes of operation: enhanceddistributed channel access (EDCA) and HCF controlled channel access(HCCA).

EDCA enhances or extends functionality of the original access DCFmethod: EDCA has been designed to support prioritized traffics similarto DiffSery (Differentiated Services), which is a protocol forspecifying and controlling network traffic by class so that certaintypes of traffic get precedence.

EDCA is the dominant channel access scheme or mechanism in WLANs becauseit features a distributed and easily deployed mechanism. The schemecontends for access to at least one communication channel of thecommunication network using contention parameters, in order for the nodeto transmit data stored locally over an accessed communication channel.

The above deficiency of failing to have satisfactory QoS due to delay inframe retransmission has been solved with a plurality of transmissionqueues/buffers.

QoS support in EDCA is achieved with the introduction of four AccessCategories (ACs), and thereby of four corresponding transmission/trafficqueues or buffers (210). Usually, the four ACs are the following indecreasing priority order: voice (or “AC_VO”), video (or “AC_VI”), besteffort (or “AC_BE”) and background (or “AC_BG”).

Of course, another number of traffic queues may be contemplated.

Each AC has its own traffic queue/buffer to store corresponding dataframes to be transmitted on the network. The data frames, namely theMSDUs, incoming from an upper layer of the protocol stack are mappedonto one of the four AC queues/buffers and thus input in the mapped ACbuffer.

Each AC has also its own set of queue contention parameters, and isassociated with a priority value, thus defining traffics of higher orlower priority of MSDUs. Thus, there is a plurality of traffic queuesfor serving data traffic at different priorities. The queue contentionparameters usually include CW_(min), CW_(max), AIFSN and TXOP_Limitparameters for each traffic queue. CW_(min) and CW_(max) are the lowerand higher boundaries of a selection range from which the EDCAcontention window CW is selected for a given traffic queue. AIFSN standsfor Arbitration Inter-Frame Space Number, and defines a number of timeslots (usually 9 μs), additional to a DIFS interval (the total definingthe AIFS period), the node must sense the medium as idle beforedecrementing the queue backoff value/counter associated with the trafficqueue considered. TXOP_Limit defines the maximum size of a TXOP the nodemay request.

That means that each AC (and corresponding buffer) acts as anindependent DCF contending entity including its respective queue backoffengine 211. Thus, each queue backoff engine 211 is associated with arespective traffic queue 210 for using queue contention parameters andsetting a respective queue backoff value/counter (randomly selected fromthe CW), to be used to contend for access to at least one communicationchannel in order to transmit data stored in the respective traffic queueover an accessed communication channel.

The contention window CW and the queue backoff value/counter are knownas EDCA variables.

It results that the ACs within the same communication node compete onewith each other to access the wireless medium and to obtain atransmission opportunity, using the conventional EDCA access scheme asexplained above for example.

Service differentiation between the ACs is achieved by setting differentqueue backoff parameters between the ACs, such as different CW_(min),CW_(max), AIFSN and/or different transmission opportunity durationlimits (TXOP_Limit). This contributes to adjusting QoS.

The usage of the AIFSN parameter and queue backoff values to access themedium in the EDCA mechanism is described below with reference to FIG. 3a.

FIG. 2 b illustrates default values for the CW_(min), CW_(max) and AIFSNparameters.

In this table, typical respective values for aCWmin and aCWmax aredefined in the above-mentioned standard as being respectively 15 and1023. Other values may be set by a node in the network (typically anAccess Point) and shared between the nodes. This information may bebroadcast in a beacon frame.

To determine the delay, AIFS[i], between the detection of the mediumbeing free and the beginning of the queue backoff value decrementing fortraffic queue T, the node multiplies the value indicated in the AIFSNparameter for traffic queue T, i.e. AIFSN[i], by a time slot duration(typically 9 micro second), and adds this value to a DIFS duration.

As shown in FIG. 3 a , it results that each traffic queue waits anAIFS[i] period (that includes the DIFS period deferring access to themedium) before decrementing its associated queue backoff value/counter.The Figure shows two AIFS[i] corresponding to two different ACs. One cansee that one prioritized traffic queue starts decrementing its backoffvalue earlier than the other less prioritized traffic queue. Thissituation is repeated after each new medium access by any node in thenetwork.

This decrementing deferring mechanism, additional to the use of anon-average lower CW, makes that high priority traffic in EDCA has ahigher chance to be transmitted than low priority traffic: a node withhigh priority traffic statistically waits a little less before it sendsits packet, on average, than a node with low priority traffic.

The EDCA queue backoff values or counters thus play two roles. First,they drive the nodes in efficiently accessing the medium, by reducingrisks of collisions. Second, they offer management of quality ofservice, QoS, by mirroring the aging of the data contained in thetraffic queue (the more aged the data, the lower the backoff value) andthus providing different priorities to the traffic queues throughdifferent values of the EDCA parameters (especially the AIFSN parameterthat delays the start of the decrementing of the EDCA queue backoffvalues).

Referring to FIG. 2 a , buffers AC3 and AC2 are usually reserved forreal-time applications (e.g., voice AC_VO or video AC_VI transmission).They have, respectively, the highest priority and the last-but-onehighest priority.

Buffers AC1 and AC0 are reserved for best effort (AC_BE) and background(AC_BG) traffic. They have, respectively, the last-but-one lowestpriority and the lowest priority.

Each data unit, MSDU, arriving at the MAC layer from an upper layer(e.g. Link layer) with a priority is mapped into an AC according tomapping rules. FIG. 3 b shows an example of mapping between eightpriorities of traffic class (User Priorities or UP, 0-7 according toIEEE 802.1d) and the four ACs. The data frame is then stored in thebuffer corresponding to the mapped AC.

When the backoff procedure for a traffic queue (or an AC) ends, the MACcontroller (reference 704 in FIG. 7 below) of the transmitting nodetransmits a data frame from this traffic queue to the physical layer fortransmission onto the wireless communication network.

Since the ACs operate concurrently in accessing the wireless medium, itmay happen that two ACs of the same communication node have theirbackoff ending simultaneously. In such a situation, a virtual collisionhandler (212) of the MAC controller operates a selection of the AChaving the highest priority (as shown in FIG. 3 b ) between theconflicting ACs, and gives up transmission of data frames from the ACshaving lower priorities.

Then, the virtual collision handler commands those ACs having lowerpriorities to start again a backoff operation using an increased CWvalue.

The QoS resulting from the use of the ACs may be signalled in the MACdata frames, for instance in a QoS control field included in the headerof the IEEE 802.11e MAC frame.

To meet the ever-increasing demand for faster wireless networks tosupport bandwidth-intensive applications, 802.11ac is targeting largerbandwidth transmission through multi-channel operations. FIG. 4 aillustrates 802.11ac channel allocation that support composite channelbandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz

IEEE 802.11ac introduces support of a restricted number of predefinedsubsets of 20 MHz channels to form the sole predefined composite channelconfigurations that are available for reservation by any 802.11ac nodeon the wireless network to transmit data.

The predefined subsets are shown in the Figure and correspond to 20 MHz,40 MHz, 80 MHz, and 160 MHz channel bandwidths, compared to only 20 MHzand 40 MHz supported by 802.11 n. Indeed, the 20 MHz component channels300-1 to 300-8 are concatenated to form wider communication compositechannels.

In the 802.11ac standard, the channels of each predefined 40 MHz, 80 MHzor 160 MHz subset are contiguous within the operating frequency band,i.e. no hole (missing channel) in the composite channel as ordered inthe operating frequency band is allowed.

The 160 MHz channel bandwidth is composed of two 80 MHz channels thatmay or may not be frequency contiguous. The 80 MHz and 40 MHz channelsare respectively composed of two frequency-adjacent or contiguous 40 MHzand 20 MHz channels, respectively. However the present invention mayhave embodiments with either composition of the channel bandwidth, i.e.including only contiguous channels or formed of non-contiguous channelswithin the operating band.

A node is granted a TXOP through the enhanced distributed channel access(EDCA) mechanism on the “primary channel” (400-3). Indeed, for eachcomposite channel having a bandwidth, 802.11ac designates one channel as“primary” meaning that it is used for contending for access to thecomposite channel. The primary 20 MHz channel is common to all nodes(STAs) belonging to the same basic set, i.e. managed by or registeredwith the same local Access Point (AP).

However, to make sure that no other legacy node (i.e. not belonging tothe same set) uses the secondary channels, it is provided that thecontrol frames (e.g. RTS frame/CTS frame) reserving the compositechannel are duplicated over each 20 MHz channel of such compositechannel.

As addressed earlier, the IEEE 802.11ac standard enables up to four, oreven eight, 20 MHz channels to be bound. Because of the limited numberof channels (19 in the 5 GHz band in Europe), channel saturation becomesproblematic. Indeed, in densely populated areas, the 5 GHz band willsurely tend to saturate even with a 20 or 40 MHz bandwidth usage perWireless-LAN cell.

Developments in the 802.11ax standard seek to enhance efficiency andusage of the wireless channel for dense environments.

In this perspective, one may consider multi-user (MU) transmissionfeatures, allowing multiple simultaneous transmissions to/from differentusers in both downlink (DL) and uplink (UL) directions with a main node,usually an AP. In the uplink, multi-user transmissions can be used tomitigate the collision probability by allowing multiple nodes tosimultaneously transmit to the AP.

To actually perform such multi-user transmission, it has been proposedto split a granted 20 MHz channel (400-1 to 400-4) into sub-channels 410(elementary sub-channels), also referred to as sub-carriers or resourceunits (RUs), that are shared in the frequency domain by multiple users,based for instance on Orthogonal Frequency Division Multiple Access(OFDMA) technique.

This is illustrated with reference to FIG. 4 .

The multi-user feature of OFDMA allows, a node, usually an access point,AP, to assign different RUs to different nodes in order to increasecompetition. This may help to reduce contention and collisions inside802.11 networks.

Contrary to MU downlink OFDMA wherein the AP can directly send multipledata to multiple nodes (supported by specific indications inside thePLCP header), a trigger mechanism has been adopted for the AP to triggerMU uplink communications from various nodes.

To support a MU uplink transmission (during a TxOP pre-empted by theAP), the 802.11ax AP has to provide signalling information for bothlegacy nodes (non-802.11ax nodes) to set their NAV and for 802.11axnodes to determine the Resource Units allocation.

In the following description, the term legacy refers to non-802.11axnodes, meaning 802.11 nodes of previous technologies that do not supportOFDMA communications.

As shown in the example of FIG. 4 , the AP sends a trigger frame (TF)430 to the targeted 802.11ax nodes. The bandwidth or width of thetargeted composite channel is signalled in the TF frame, meaning thatthe 20, 40, 80 or 160 MHz value is signalled. The TF frame is sent overthe primary 20 MHz channel and duplicated (replicated) on each other 20MHz channels forming the targeted composite channel. As described abovefor the duplication of control frames, it is expected that every nearbylegacy node (non-HT or 802.11ac nodes) receiving the TF frame (or aduplicate thereof) on its primary channel, then sets its NAV to thevalue specified in the TF frame. This prevents these legacy nodes fromaccessing the channels of the targeted composite channel during theTXOP.

Based on an AP's decision, the trigger frame TF may define a pluralityof resource units (RUs) 410, or “Random RUs”, which can be randomlyaccessed by the nodes of the network. In other words, Random RUsdesignated or allocated by the AP in the TF may serve as basis forcontention between nodes willing to access the communication medium forsending data. A collision occurs when two or more nodes attempt totransmit at the same time over the same RU.

In that case, the trigger frame is referred to as a trigger frame forrandom access (TF-R). A TF-R may be emitted by the AP to allow multiplenodes to perform MU UL (Multi-User UpLink) random access to obtain an RUfor their UL transmissions.

The trigger frame TF may also designate Scheduled resource units, inaddition to or in replacement of the Random RUs. Scheduled RUs may bereserved by the AP for certain nodes in which case no contention foraccessing such RUs is needed for these nodes. Such RUs and theircorresponding scheduled nodes are indicated in the trigger frame. Forinstance, a node identifier, such as the Association ID (AID) assignedto each node upon registration, is added, in the TF frame, inassociation with each Scheduled RU in order to explicitly indicate thenode that is allowed to use each Scheduled RU.

An AID equal to 0 may be used to identify random RUs.

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent nodes in order to increase competition. This may help toreduce contention and collisions inside 802.11 networks.

In the example of FIG. 4 , each 20 MHz channel (400-1, 400-2, 400-3 or400-4) is sub-divided in the frequency domain into four sub-channels orRUs 410, typically of size 5 Mhz.

Of course the number of RUs splitting a 20 MHz channel may be differentfrom four. For instance, between two to nine RUs may be provided (thuseach having a size between 10 MHz and about 2 MHz).

Once the nodes have used the RUs to transmit data to the AP, the APresponds with an acknowledgment ACK (not show in the Figure) toacknowledge the data on each RU, making it possible for each node toknow when its data transmission is successful (reception of the ACK) ornot (no ACK after expiry of a time-out).

Document IEEE 802.11-15/1105 provides an exemplary random allocationprocedure that may be used by the nodes to access the Random RUsindicated in the TF. This random allocation procedure, referred to as RUcontention scheme, is managed by a dedicated RU access module separatefrom the above-mentioned channel access module and is configured tomanage access to at least one resource unit provided by another node(usually the AP) within a transmission opportunity granted to the othernode on the communication channel, in order to transmit data storedlocally over an accessed resource unit. Preferably, the RU access moduleincludes an RU backoff engine separate from the queue backoff engines,which uses RU contention parameters, including a computed RU backoffvalue, to contend for access to the random RUs.

In other words, the RU contention scheme is based on a new backoffcounter, referred to as the OFDMA or RU backoff counter/value (or OBO),inside the 802.11ax nodes for allowing a dedicated contention whenaccessing a random RU to send data.

Each node STA1 to STAn is a transmitting node with regards to receivingAP, and as a consequence, each node has an active RU backoff engineseparate from the queue backoff engines, for computing an RU backoffvalue (OBO) to be used to contend for access to at least one randomresource unit splitting a transmission opportunity granted on thecommunication channel, in order to transmit data stored in eithertraffic queue AC.

The random allocation procedure in this document comprises, for a nodeof a plurality of nodes having an active RU backoff value OBO, a firststep of determining from the trigger frame the random sub-channels orRUs of the communication medium available for contention, a second stepof verifying if the value of the active RU backoff value OBO local tothe considered node is not greater than a number ofdetected-as-available random RUs, and then, in case of successfulverification, a third step of randomly selecting a random RU among thedetected-as-available random RUs for sending data. In case the secondstep is not verified, a fourth step (instead of the third) is performedin order to decrement the RU backoff value OBO by the number ofdetected-as-available RUs.

As shown in the Figure, some Resource Units may not be used (410 u)because no node with an RU backoff value OBO less than the number ofavailable random RUs has randomly selected one of these random RUs,whereas some other have collided (as example 410c) because two of thesenodes have randomly selected the same RU.

The MU Uplink (UL) medium access scheme, including both scheduled RUsand random RUs, proves to be very efficient compared to conventionalEDCA access scheme. This is because the number of collisions generatedby simultaneous medium access attempts and the overhead due to themedium access are both reduced.

However, the EDCA access scheme and MU UL OFDMA/RU access scheme have tocoexist, in particular to allow legacy 802.11 nodes to access the mediumand to allow even the 802.11ax nodes to initiate communication withnodes other than the AP.

Although the EDCA access scheme taken alone provides a fair access tothe medium throughout all the nodes, its association with the MU ULOFDMA/RU access scheme introduces a drift in fairness. This is because,compared to the legacy nodes, the 802.11ax nodes have additionalopportunities to send data through the resource units offered in thetransmission opportunities granted to another node, in particular to theAP.

To restore some fairness between the nodes, solutions have beenproposed,

For instance in co-pending UK application No 1612151.9 filed on 13 Jul.2016, a current value of at least one EDCA parameter is modified intodifferent values (MU EDCA parameters), upon successfully transmittingdata over an accessed resource unit (i.e. through UL OFDMAtransmission). This is to reduce a probability for the node to access acommunication channel through (conventional EDCA) contention.

In this framework, a mechanism has been proposed to reduce the node'sprobability of EDCA-based transmission (i.e. using the EDCA mediumaccess scheme) as soon as the node successfully uses the MU UL mechanismto transmit its data. This reduction is made by modifying the well-knownEDCA parameters.

The proposed mechanism, as described in document IEEE 802.11-16/1180entitled “Proposed text changes for MU EDCA parameters”, sets eachtransmitting traffic queue in a MU EDCA mode in response to successfullytransmitting the data in the accessed MU UL OFDMA resource unit. Thesetting is done for a predetermined duration, known as HEMUEDCATimer.The MU EDCA mode is a mode in which the respective EDCA parameters areset to MU values different from legacy values used in a different legacyEDCA mode.

To switch from legacy EDCA contention access mode to the MU EDCA mode,the node may modify its EDCA parameters (AIFSN, CW_(min), and/orCW_(max)) for all the traffic queues having successfully transmittedsome data in the accessed resource unit. The switch back to the legacyEDCA mode may occur upon expiry of the HEMUEDCATimer, being noted thatthis timer is reset to its initial value each time the node transmitsagain new data (from either AC) during newly accessed resource unitsprovided by the AP. The initializing value of HEMUEDCATimer is suggestedto be high (e.g. tens of milliseconds) in order to encompass several newopportunities for MU UL transmissions.

The MU values for the EDCA parameters may be transmitted by the AP in aDedicated Information Element, typically sent within a beacon framebroadcasting network information to the nodes.

The disclosed approach suggests increasing only the value of AIFSN foreach transmitting traffic queue, while keeping CW_(min), and CW_(max)unchanged. As the corresponding AIFS period increases, each trafficqueue in the MU EDCA mode is prevented (or at least substantiallydelayed) from having its queue backoff value or counter been decrementedupon sensing the medium free again. New accesses to the medium usingEDCA access scheme are statistically substantially reduced, or even nolonger possible, during the above-mentioned predetermined duration.

The MU-mode AIFSN value may be very restrictive. So, in high densityenvironment where the medium is busy most of the time (and thus remainfree for very short time), the node in MU EDCA mode must wait for thecorresponding very restrictive AIFS period, and thus does not decrementthe backoff value of the AC queue in MU EDCA mode very often. The resultis that the node cannot EDCA-contend for access to the medium veryoften.

Note that a specific configuration in the publication tends to totallyprevent (except if the network is not used at all) the transmittingtraffic queues from EDCA-accessing the medium while in the MU EDCA mode.The AP specifies this particular operating mode by indicating a specificvalue of the AIFSN parameter (typically 0) in the set of MU EDCAparameters. Such specific value means for the node that it shall use avery high value for its AIFSN, which value is equal to the HEMUEDCATimeras transmitted by the AP (it is reminded its value should be high, abouttens of milliseconds, to be compared to less than 0.1 millisecond forthe worst AIFS[i] in the legacy EDCA mode).

Unfortunately, as long as the node regularly accesses OFDMA RUs totransmit data, its traffic queues in the MU EDCA mode remain in the sameMU mode. This applies in particular for those traffic queues in the MUmode that do not even send any data in the accessed OFDMA RUs over apotential lengthy period of regular OFDMA accesses. This is contrary tothe QoS principle as described in the 802.11e standard.

This situation is now illustrated with reference to FIG. 5 a whichdescribes an example of application using MU EDCA parameters asdescribed in the above-mentioned publication.

In the scenario of this Figure, the AP 501 polls a node 502 by sending astandardized Trigger Frame 1300 requesting the node to transmit some QoSdata coming from the AC_VI access category. This may be done byproviding one or more Scheduled RUs to that node. The category may beindicated in the “Preferred AC” field 1330 shown in FIG. 13 .

After a SIFS time, node 502 initiates a MU UL OFDMA transmission 510 bypicking up some QoS data (511) from solicited traffic queue AC_VI. Inthis exemplary scenario, there is not enough QoS data ready to be sentin the solicited traffic queue AC_VI. In this context, node 502 isallowed to retrieve other QoS data (512) from a higher-priority trafficqueue, for instance the AC_VO access category in the example. This dataretrieval rule makes it possible to maximize bandwidth usage asspecified in the 802.11 standard.

Thus, node 502 transmits AC_VI data 511 and AC_VO data 512 to the APusing the scheduled RU. The corresponding two transmitting trafficqueues, AC_VI and AC_VO, thus switch to the MU EDCA mode (symbolized bywhite figures in black boxes), in which node 502 now uses MU EDCAparameters for each of these transmitting traffic queues. Particularly,higher values for the AIFSN parameter may be used, and optionally forthe CW_(min) and CW_(min) parameters.

In parallel, the HEMUEDCATimer 590 is launched to count down when node502 will be allowed to switch back to the legacy EDCA mode with legacyEDCA parameters. The switch back may occur after a predeterminedduration expires, i.e. when the HEMUEDCATimer reaches 0.

However, the HEMUEDCATimer is reinitialized to its initial value (thepredetermined duration) each time node 502 transmits data in an accessedresource unit provided by the AP within any subsequent transmissionopportunity granted to the AP on the communication channel. In otherwords, the timer is reinitialized each time node 502 is polled again bythe AP.

This occurs in the example of FIG. 5 a when AP 501 sends a new triggerframe 1300-2 with a new RU for node 502, while the HEMUEDCATimer 590 hasnot yet expired. The AP again polls node 502 to send QoS data from AC_VIaccess category.

Node 502 again transmits QoS data 520 from the AC_VI access category andthe HEMUEDCATimer 590 is reinitialized to its initial value, thepredetermined duration. The same occurs when AP 501 polls again node 502to send new QoS data from AC_VI access category, by sending a newtrigger frame 1300-3.

In this scenario, node 502 is regularly polled by the AP for OFDMAtransmission of QoS data from AC_VI. Finally, as long as enough data areprovided by the AC_VI category, the AC_VO category is never involved ina new OFDMA transmission and remains blocked in the MU EDCA mode.

In addition, due to its MU-mode AIFSN value (usually more restrictivevalue, i.e. high value), the traffic queue AC_VO is prevented (orseverely delayed) from decrementing the associated backoff value forEDCA-contending the medium.

It results that the AC_VO category, which by essence has the highest QoSpriority, remains locked in the MU EDCA mode without having new EDCAopportunities to send its data. The QoS requirements of 802.11ax thusremain severely deteriorated.

It is within this framework that the present invention proposes torestore QoS fairness by breaking the unicity of the HEMUEDCATimer bywhich the traffic queues in MU mode are locked in case of regular nodepolling by the AP.

In particular, upon (preferably successfully) transmitting data storedin two or more traffic queues, in each of one or more accessed resourceunits provided by another node within one or more transmissionopportunities granted to the other node on the communication channel,node 502 may set each transmitting traffic queue (i.e. transmitting inthe accessed resource unit) in a MU EDCA mode, different from the legacyEDCA mode, for a predetermined duration counted down by a respectivetimer associated with the transmitting traffic queue. Next, upon expiryof any timer, node 502 may switch back the associated traffic queue tothe legacy EDCA mode in which the respective EDCA parameters are setback to the legacy values.

The present invention thus provides the node with a plurality of timers,each one being associated with one of the traffic queues. As a specificHEMUEDCATimer is dedicated for each AC queue, the latter can exit the MUEDCA mode independently of the other AC queues. QoS at AC queue level isthus restored.

The result of one implementation of the present invention is nowillustrated with reference to FIG. 5 b which describes, with the samesequence as in FIG. 5 a , the restoring of QoS through the handling ofindependent HEMUEDCATimers.

After the first TF 1300, both transmitting traffic queues, AC_VI andAC_VO, are in the MU EDCA mode. Their respective HEMUEDCATimer, 591 forAC_VI and 592 for AC_VO, are started simultaneously to count down wheneach respective traffic queue is allowed to switch back to the legacyEDCA mode with legacy EDCA parameters.

According to the invention, the evolving of these separate timers isindependent one of the other.

As explained below, different predetermined durations may be used toinitialize the two timers associated with AC_VI and AC_VO. This is toimprove the QoS management.

Thus, when the next TF 1300-2 is received and AC_VI data are transmittedin the accessed OFDMA RU as required by the AP, HEMUEDCATimer 591associated with AC_VI is reinitialized with its corresponding initialpredetermined duration, while HEMUEDCATimer 592 associated with AC_VOcontinues elapsing (because no VO data have been transmitted in theaccessed RU following TF 1300-2).

As a consequence, HEMUEDCATimer 592 associated with AC_VO expires beforeHEMUEDCATimer 591 associated with AC_VI, loosening the MU EDCAconstraints on traffic queue AC_VO. Practically, traffic queue AC_VO isswitched back to the legacy EDCA mode in which legacy EDCA parametersare used. The backoff value of the AC_VO traffic queue can thus bedecreased as normal way allowing the AC_VO queue to efficiently contendthe medium.

FIG. 6 schematically illustrates a communication device 600 of the radionetwork 100, configured to implement at least one embodiment of thepresent invention. The communication device 600 may preferably be adevice such as a micro-computer, a workstation or a light portabledevice. The communication device 600 comprises a communication bus 613to which there are preferably connected:

-   -   a central processing unit 611, such as a microprocessor, denoted        CPU;    -   a read only memory 607, denoted ROM, for storing computer        programs for implementing the invention;    -   a random access memory 612, denoted RAM, for storing the        executable code of methods according to embodiments of the        invention as well as the registers adapted to record variables        and parameters necessary for implementing methods according to        embodiments of the invention; and    -   at least one communication interface 602 connected to the radio        communication network 100 over which digital data packets or        frames or control frames are transmitted, for example a wireless        communication network according to the 802.11ax protocol. The        frames are written from a FIFO sending memory in RAM 612 to the        network interface for transmission or are read from the network        interface for reception and writing into a FIFO receiving memory        in RAM 612 under the control of a software application running        in the CPU 611.

Optionally, the communication device 600 may also include the followingcomponents:

-   -   a data storage means 604 such as a hard disk, for storing        computer programs for implementing methods according to one or        more embodiments of the invention;    -   a disk drive 605 for a disk 606, the disk drive being adapted to        read data from the disk 606 or to write data onto said disk;    -   a screen 609 for displaying decoded data and/or serving as a        graphical interface with the user, by means of a keyboard 610 or        any other pointing means.

The communication device 600 may be optionally connected to variousperipherals, such as for example a digital camera 608, each beingconnected to an input/output card (not shown) so as to supply data tothe communication device 600.

Preferably the communication bus provides communication andinteroperability between the various elements included in thecommunication device 600 or connected to it. The representation of thebus is not limiting and in particular the central processing unit isoperable to communicate instructions to any element of the communicationdevice 600 directly or by means of another element of the communicationdevice 600.

The disk 606 may optionally be replaced by any information medium suchas for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, aUSB key or a memory card and, in general terms, by an informationstorage means that can be read by a microcomputer or by amicroprocessor, integrated or not into the apparatus, possibly removableand adapted to store one or more programs whose execution enables amethod according to the invention to be implemented.

The executable code may optionally be stored either in read only memory607, on the hard disk 604 or on a removable digital medium such as forexample a disk 606 as described previously. According to an optionalvariant, the executable code of the programs can be received by means ofthe communication network 603, via the interface 602, in order to bestored in one of the storage means of the communication device 600, suchas the hard disk 604, before being executed.

The central processing unit 611 is preferably adapted to control anddirect the execution of the instructions or portions of software code ofthe program or programs according to the invention, which instructionsare stored in one of the aforementioned storage means. On powering up,the program or programs that are stored in a non-volatile memory, forexample on the hard disk 604 or in the read only memory 607, aretransferred into the random access memory 612, which then contains theexecutable code of the program or programs, as well as registers forstoring the variables and parameters necessary for implementing theinvention.

In a preferred embodiment, the apparatus is a programmable apparatuswhich uses software to implement the invention. However, alternatively,the present invention may be implemented in hardware (for example, inthe form of an Application Specific Integrated Circuit or ASIC).

FIG. 7 is a block diagram schematically illustrating the architecture ofa communication device or node 600, in particular one of nodes 100-107,adapted to carry out, at least partially, the invention. As illustrated,node 600 comprises a physical (PHY) layer block 703, a MAC layer block702, and an application layer block 701.

The PHY layer block 703 (here an 802.11 standardized PHY layer) has thetask of formatting frames, modulating frames on or demodulating framesfrom any 20 MHz channel or the composite channel, and thus sending orreceiving frames over the radio medium used 100. The frames may be802.11 frames, for instance medium access trigger frames TF 430 todefine resource units in a granted transmission opportunity, MAC dataand management frames based on a 20 MHz width to interact with legacy802.11 stations, as well as of MAC data frames of OFDMA type havingsmaller width than 20 MHz legacy (typically 2 or 5 MHz) to/from thatradio medium.

The MAC layer block or controller 702 preferably comprises a MAC 802.11layer 704 implementing conventional 802.11ax MAC operations, and anadditional block 705 for carrying out, at least partially, theinvention. The MAC layer block 702 may optionally be implemented insoftware, which software is loaded into RAM 512 and executed by CPU 511.

Preferably, the additional block, referred to as MU EDCA mode managementmodule 705 implements the part of the invention that regards node 600,i.e. managing the switching between the two legacy and MU EDCA modes,and handling the various timers used to control each traffic queue inthe MU EDCA mode.

From the AP perspective, this MU EDCA mode management module 705 may beprovided to send, to the nodes, the set of legacy values of the EDCAparameters and the set of MU values of the EDCA parameters, differentfrom the set of legacy values, and a set of initializing values for theHEMUEDCATimers to drive the nodes entering the MU EDCA mode to remain insuch mode at least the corresponding duration. These values thus driveeach node in configuring itself when one of its traffic queues switchesbetween a legacy EDCA mode in which the respective EDCA parameters areset to the legacy values and a MU EDCA mode, to be maintained during apredetermined duration initialized based on the associated initializingvalue and counted down by an associated timer, in which the respectiveEDCA parameters are set to the MU values.

MAC 802.11 layer 704 and MU EDCA mode management module 705 interact onewith the other in order to provide management of the channel accessmodule handling the queue backoff engines and a RU access modulehandling the RU backoff engine as described below.

On top of the Figure, application layer block 701 runs an applicationthat generates and receives data packets, for example data packets of avideo stream. Application layer block 701 represents all the stacklayers above MAC layer according to ISO standardization.

Embodiments of the present invention are now illustrated using variousexemplary embodiments. Although the proposed examples use the triggerframe 430 (see FIG. 4 ) sent by an AP for a multi-user uplinktransmissions, equivalent mechanisms can be used in a centralized or inan ad-hoc environment (i.e. without an AP). It means that the operationsdescribed below with reference to the AP may be performed by any node inan ad-hoc environment.

These embodiments are mainly described in the context of IEEE 802.11axby considering OFDMA resource units. Application of the invention ishowever not limited to the IEEE 802.11ax context.

Also the present invention does not necessarily rely on the usage of aMU access scheme as described in 802.11ax. Any other RU access schemedefining alternate medium access schemes allowing simultaneous access bythe nodes to the same medium can also be used.

The set of MU values may be more restrictive than the set of legacyvalues, resulting for a traffic queue being in the MU EDCA mode toaccess less often the medium using EDCA contention access scheme.

However, the set of MU values may be more permissive in someembodiments.

For the sake of clarity, the explanations below focus on a set of MUvalues that is more restrictive. In this context, the MU EDCA mode isreferred to as the “degraded” mode, while the legacy EDCA mode isreferred to as “non-degraded” mode.

FIG. 8 illustrates an exemplary transmission block of a communicationnode 600 according to embodiments of the invention.

As mentioned above, the node includes a channel access module andpossibly an RU access module, both implemented in the MAC layer block702. The channel access module includes:

a plurality of traffic queues 210 for serving data traffic at differentpriorities;

a plurality of queue backoff engines 211, each associated with arespective traffic queue for using EDCA parameters, in particular forcomputing a respective queue backoff value, to be used to contend foraccess to at least one communication channel in order to transmit datastored in the respective traffic queue. This is the EDCA access scheme.

According to embodiments of the present invention, each queue backoffengine 211 has its own HEMUEDCATimer 2110. It means the node comprises aplurality of timers, each one associated with one of the traffic queues.

Also an EDCA mode switch 213 is provided in the node that handles theswitching between the degraded MU EDCA mode and the legacy EDCA mode, byupdating the EDCA parameters according to the teachings of theinvention. The EDCA mode switch operates responsive to each OFDMAtransmission in a RU by the node.

The RU access module includes an RU backoff engine 800 separate from thequeue backoff engines, for using RU contention parameters, in particularfor computing an RU backoff value, to be used to contend for access tothe OFDMA random resource units defined in a received TF (sent by the APfor instance), in order to transmit data stored in either traffic queuein an OFDMA RU. The RU backoff engine 800 is associated with atransmission module, referred to as OFDMA muxer 801. For example OFDMAmuxer 801 is in charge, when the RU backoff value OBO described belowreaches zero, of selecting data to be sent from the AC queues 210.

The conventional AC queue back-off registers 211 drive the medium accessrequest along EDCA protocol (channel contention access scheme), while inparallel, the RU backoff engine 800 drives the medium access requestonto OFDMA multi-user protocol (RU contention access scheme).

As these two contention access schemes coexist, the source nodeimplements a medium access mechanism with collision avoidance based on acomputation of backoff values:

-   -   a queue backoff counter value corresponding to a number of        time-slots the node waits (in addition to a DIFS period), after        the communication medium has been detected to be idle, before        accessing the medium. This is EDCA, regardless of whether it is        in a degraded or non-degraded state;    -   an RU backoff counter value (OBO) corresponding to a number of        idle random RUs the node detects, after a TXOP has been granted        to the AP or any other node over a composite channel formed of        RUs, before accessing the medium. This is OFDMA. A variant to        counting down the OBO based on the number of idle random RUs may        be based on a time-based countdown.

FIG. 9 illustrates, using a flowchart, main steps performed by MAC layer702 of node 600, when receiving new data to transmit. It illustrates aconventional FIFO feeding in 802.11 context.

At the very beginning, none traffic queue 210 stores data to transmit.As a consequence, no queue backoff value 211 has been computed. It issaid that the corresponding queue backoff engine or corresponding AC(Access Category) is inactive. As soon as data are stored in a trafficqueue, a queue backoff value is computed (from corresponding queuebackoff parameters), and the associated queue backoff engine or AC issaid to be active.

When a node has data ready to be transmitted on the medium, the data arestored in one of the AC queue 210, and the associated backoff 211 shouldbe updated.

At step 901, new data are received from an application running on thedevice (from application layer 701 for instance), from another networkinterface, or from any other data source. The new data are ready to besent by the node.

At step 902, the node determines in which AC queues 210 the data shouldbe stored. This operation is usually performed by checking the TID(Traffic Identifier) value attached to the data (according to thematching shown in FIG. 3 b ).

Next, step 903 stores the data in the determined AC queue. It means thedata are stored in the AC queue having the same data type as the data.

At step 904, conventional 802.11 AC backoff computation is performed bythe queue backoff engine associated with the determined AC queue.

If the determined AC queue was empty just before the storage of step 903(i.e. the AC is originally inactive), then there is a need to compute anew queue backoff value for the corresponding backoff counter.

The node thus computes the queue backoff value as being equal to arandom value selected in range [0, CW], where CW is the current value ofthe CW for the Access Category considered (as defined in 802.11standard). It is recalled here that the queue backoff value will beadded to the AIFSN (which may be degraded in the MU EDCA mode) in orderto implement the relative priorities of the different access categories.CW is a congestion window value that is selected from selection range[CW_(min), CW_(max)], where both boundaries CW_(min) and CW_(max)(possibly degraded) depend on the Access Category considered.

As a result the AC is made active.

The above parameters CW, CW_(min), CW_(max), AIFSN, and Backoff valueform the EDCA parameters and variables associated with each AC. They areused to set the relative priorities to access the medium for thedifferent categories of data.

The EDCA parameters have usually a fixed value (e.g. CW_(min), CW_(max),and AIFSN), while the EDCA variables (CW and backoff value) evolve overtime and medium availability. As readily apparent from the above, thepresent invention provides evolution of the EDCA parameters through theswitching between degraded and non-degraded parameter values.

Also step 904 may include computing the RU backoff value OBO if needed.An RU backoff value OBO needs to be computed if the RU backoff engine800 was inactive (for instance because there were no data in the trafficqueues until previous step 903) and if new data to be addressed to theAP have been received.

The RU backoff value OBO may be computed in a similar fashion as theEDCA backoff value, i.e. using dedicated RU contention parameters, suchas a dedicated contention window [0, CWO] and a selection range[CWO_(min), CWO_(max)].

Note that some embodiments may provide distinction between data that canbe sent through resource units (i.e. compatible with MU UL OFDMAtransmission) and those that cannot. Such decision can be made duringstep 902, and a corresponding marking item can be added to the storeddata.

In such a case, the RU backoff value OBO is computed only if the newlystored data are marked as compatible with MU UL OFDMA transmission.

Next to step 904, the process of FIG. 9 ends.

Once data are stored in the AC queues, the node may access the mediumdirectly through EDCA access scheme (either with the legacy EDCA mode orwith the degraded MU EDCA mode) as illustrated below with reference toFIG. 10 , or through resource units provided by the AP through one ormore trigger frames, as illustrated below with reference to FIG. 11 .

FIG. 10 illustrates, using a flowchart, steps of accessing the mediumbased on the (legacy or degraded MU) EDCA medium access scheme.

Steps 1000 to 1020 describe a conventional waiting introduced in theEDCA mechanism to reduce the collision on a shared wireless medium. Instep 1000, node 600 senses the medium waiting for it to become available(i.e. detected energy is below a given threshold on the primarychannel).

When the medium becomes free during an AIFS[i] period (including a DIFSperiod and the AIFSN[i] period—see FIG. 3 a ), step 1010 is executed inwhich node 600 decrements all the active (non-zero) AC[ ] queue backoffcounters 211 by one. In other words, the node decrements the queuebackoff values each elementary time unit the communication channel isdetected as idle.

Next, at step 1020, node 600 determines if at least one of the ACbackoff counters reaches zero.

If no AC queue backoff reaches zero, node 600 waits for another backofftimeslot (typically 9 μs), and thus loops back to step 1000 in order tosense the medium again during the next backoff timeslot. This makes itpossible to decrement the AC backoff counters at each new backofftimeslot when the medium is sensed as idle, as soon as their respectiveAIFS[i] have expired.

If at least one AC queue backoff reaches zero, step 1030 is executed inwhich node 600 (more precisely virtual collision handler 212) selectsthe active AC queue having a zero queue backoff counter and having thehighest priority.

At step 1040, an appropriate amount of data is selected from thisselected AC for transmission, to match the bandwidth of the TXOP.

Next, at step 1050, node 600 initiates an EDCA transmission, in case forinstance an RTS/CTS exchange has been successfully performed to have aTXOP granted. Node 600 thus sends the selected data on the medium,during the granted TXOP.

Next, at step 1060, node 600 determines whether or not the EDCAtransmission has ended, in which case step 1070 is executed.

At step 1070, node 600 updates the contention window CW of the selectedtraffic queue, based on the status of transmission (positive or negativeack, or no ack received). Typically, node 600 doubles the value of CW ifthe transmission failed, until CW reaches the maximum value CW_(max)(either degraded or not) which depends on the AC type of the data. Onthe other hand, if the EDCA transmission is successful, the contentionwindow CW is set to the minimum value CW_(min) (either degraded or not)which is also dependent on the AC type of the data.

Next, if the selected traffic queue is not empty after the EDCA datatransmission, a new associated queue backoff counter is randomlyselected from [0,CW], similar to step 904.

This ends the process of FIG. 10 .

FIG. 11 illustrates, using a flowchart, steps of accessing resourceunits based on an RU or OFDMA access scheme upon receiving a triggerframe defining RUs. For instance, this illustrates node 502's behaviorin FIG. 5 b.

At step 1110, the node determines whether a trigger frame is receivedfrom the access point in the communication network, the trigger framereserving a transmission opportunity granted to the access point on thecommunication channel and defining resource units, RUs, forming thecommunication channel. If so, the node analyses the content of thereceived trigger frame.

At step 1120, the node determines whether or not it can transmit dataover one of the RUs defined in the received trigger frame. Thedetermination may involve one or both of two conditions, regarding inparticular the type of RUs.

By analysing the content of the received TF, the node determines whetheror not a defined RU is a scheduled resource unit assigned by the accesspoint to the node. This may be done by looking for its own AID in thereceived TF, which AID is associated with a specific scheduled RU to beused for MU UL OFDMA transmission.

Also, by analysing the content of the received TF, the node determineswhether or not one or more random RUs are defined in the TF, i.e. RUsthe access of which is made through contention using dedicated RUcontention parameters (including the above-mentioned OBO value 800). Inthat case, the node also determines whether or not its current OBO value800 allows one random RU to be selected (for instance if OBO 800 is lessthan the number of random RUs in the TF).

If one scheduled RU is assigned to the node or the latter is allowed(after contention) to access one random RU, the node determines the sizeof the random/scheduled RU or RUs to be used and step 1130 is executed.Otherwise, the node decrements the RU backoff value OBO 800 based on thenumber of random resource units defined in the received trigger frame,and the process ends as the node cannot access any RU defined by thereceived TF.

At step 1130, the node selects at least one of the traffic queues 210from which the data to be transmitted are selected, and adds data of theselected queue or queues to the transmission buffer until the quantityof data reaches the size of the selected resource unit to be used.

Various criteria to select a current traffic queue may be involved.

For instance, this may be done by:

selecting a traffic queue 210 having the lowest associated queue backoffvalue. The selection of the traffic queue thus depends on the values ofthe EDCA backoffs 211, thereby guaranteeing that the node respects theEDCA principle and that correct QoS is implemented for its data);

selecting randomly one non-empty traffic queue from the traffic queues;

selecting a traffic queue storing the biggest amount of data (i.e. themost loaded);

selecting a non-empty traffic queue having the highest associatedtraffic priority (given the AC categories shown in FIG. 3 b );

selecting a non-empty traffic queue associated with a data type matchinga data type associated with the resource unit over which the data toselect are to be transmitted. Such specified data type may be a trafficqueue indicated by the AP in the trigger frame, for instance using thePreferred AC field 1340 of FIG. 13 when the AC Preference Level field isset to 1, This is the selection criteria used in the example of FIG. 5b.

Next to step 1130, step 1140 provides that the node sets or updates alist of emitting/transmitting queues by inserting the current trafficqueue from which the data selected in step 1130 come. The list keeps theorder of insertion of the emitting/transmitting queues, so that forinstance a primary emitting/transmitting queue (first queue selected onstep 1030) and subsequent emitting/transmitting queues can be easilyidentified.

In addition, the node may store during step 1140 an item of informationrepresenting the amount of data thus selected from the current trafficqueue, for transmission in the RU. For instance, then node updates thelist of emitting queues by also inserting the quantity of data selectedfrom the current traffic queue.

This list of emitting/transmitting queues can be implemented through atable containing for each traffic queue, the rank of the transmittingqueue (which may be simplified to “primary” or “secondary” queue) andthe quantity of data put in the transmission buffer.

At step 1150, the node determines whether or not the amount of datastored in the transmission buffer is enough to fill the selectedresource unit.

If not, there is still room for additional data in the resource unit.Thus the process loops back to step 1130 during which another trafficqueue may be selected, using the same selection criteria. In such a way,the transmission buffer is progressively filled up to reach the selectedresource unit size.

One may thus note that a plurality of transmitting traffic queues of thesame node may be involved during a MU UL OFDMA transmission, therebyresulting in having the plurality of queues entering the MU EDCA mode.

In a variant which avoids mixing data from two or more traffic queues(i.e. the data for the selected RU are selected from a single trafficqueue), padding data may be added to entirely fill the selected RU. Thisis to ensure the whole RU duration has energy that can be detected bylegacy nodes.

In another variant implementing a specific data aggregation rule, if thefirst selected traffic queue has not data enough to fully fill in theaccessed resource unit, data from higher priority traffic queues may beselected.

Once, the transmission buffer is full for the selected RU, step 1160initiates the MU UL OFMDA transmission of the data stored in thetransmission buffer, to the AP. The OFDMA transmission is based on theOFDMA sub-channel and modulation defined in the received trigger frameand especially in the RU definition.

Next, once the transmission has been performed, and preferably uponsuccessful transmission (i.e. an acknowledgment is received from theAP), step 1170 determines the new value or values to be applied to oneor more EDCA parameters of the traffic queue or queues, in order tomodify it or them into penalized value or values.

The transmitting queues added in the list at step 1140 thus enter the MUEDCA mode, meaning that their EDCA or “queue contention” parameter setshould be modified, in particular into degraded parameter values to bedetermined. One or more transmitting queues may already be in the MUEDCA mode. However, the degraded parameter values are also to bedetermined (they may be modified by a beacon frame recently receivedwith new degraded values).

During step 1170, the degraded parameter values are determined.

In embodiments, the degraded values of the EDCA parameters include adegraded Arbitration Inter-Frame Space Number, AIFSN, compared tonon-degraded values of the EDCA parameters used for the traffic queuenot set in the MU EDCA mode. In other words, the AIFSNs of thetransmitting queues are set to degraded values.

In some embodiments, AIFSN is the only one parameter modified whenswitching into the MU EDCA mode. It means the degraded values of theEDCA parameters include the same lower boundary CW_(min) and/or higherboundary CW_(max) as the non-degraded values used for legacy EDCA mode,both CW_(min) and CW_(max) defining a selection range from which a sizeof the contention window is selected.

The degraded values used for this step are preferably selected in thelast received Dedicated Information Element, usually forming part of abeacon frame transmitted by the AP. Thus, for a node periodicallyreceiving a beacon frame from the access point, each beacon framebroadcasting network information about the communication network to theplurality of nodes, a received beacon frame thus includes, usually inaddition to non-degraded (or legacy EDCA) values, the degraded valuesfor the EDCA parameters of the plurality of traffic queues switchinginto the MU EDCA mode.

If such degraded values are not received from the AP, by-default valuesas described in the standard may be used.

Step 1170 also includes determining the predetermined degrading durationHEMUEDCATimer[AC] value for each transmitting traffic queue AC. Thisduration defines the period during which the node must remain in the MUEDCA mode for the associated degraded traffic queue. This informationmay also be obtained from the AP, for instance from a specific DedicatedInformation Element of a received beacon frame as depicted in FIG. 14 bor 14 c below.

Next to step 1170, step 1180 actually replaces the current values of theEDCA parameters associated with the transmitting traffic queue(s) by thedegraded values determined at step 1170.

In case parameters CW_(min) and/or CW_(max) have new values, the currentCW of one or more traffic queues may be out-of-date. In that case, a newCW may be selected from newly defined range [CW_(min), CW_(max)].

Next, at step 1190, the timer 2110 associated with each transmittingtraffic queue 210 is initialized by the respective predetermineddegrading duration HEMUEDCATimer[AC] as determined at step 1170. Thetimer 2110 is then launched and progressively elapses as the time goes.

Note that if the timer was already elapsing when step 1180 is performed(meaning the associated traffic queue was already in the MU EDCA mode),the timer is reinitialized (i.e. reset) again to the HEMUEDCATimer[AC]value in order to keep the node in MU EDCA mode for a nextHEMUEDCATimer[AC] period. This is the case of timer 591 in the exampleof FIG. 5 b,

FIG. 12 illustrates, using a flowchart, the node management at queuelevel to switch back to the non-degraded legacy mode in the examplesabove. This management is based on the HEMUEDCATimer[AC] dedicated tothe traffic queue AC concerned. Indeed, the traffic queue AC may remainin the MU EDCA mode as long as this timer HEMUEDCATimer[AC] has notlapsed.

Thus at step 1210, it is checked whether or not HEMUEDCATimer[AC] haslapsed/expired, i.e. has reached the value 0.

In the affirmative, the traffic queue AC is switched back to the EDCAmode at step 1220. This may include resetting the EDCA parameters tonon-degraded values, for instance as those provided by the AP to thenodes using the beacon frame of FIG. 14 a below.

Note that due to the re-initialization of the timer at each new step1190, the expiry of HEMUEDCATimer[AC] only occurs when no data fromtraffic queue AC is transmitted, from the node, in any OFDMA resourceunit provided by the AP within subsequent TXOPs granted to the AP duringthe predetermined degrading duration.

Next, the process ends at step 1230.

The process of FIG. 12 is performed in parallel and independently foreach traffic queue in the degraded MU EDCA mode (i.e. for which a timeris elapsing). This is because the timers 2110 are separate according tothe teachings of the invention.

FIG. 13 illustrates the structure of a trigger frame as defined in the802.11ax draft standard.

The trigger frame 1300 is composed of a dedicated field 1310 called UserInfo Field. This field contains a “Trigger dependent Common info” field1320 which contains the “AC Preference Level” field 1330 and “PreferredAC” field 1340.

The Preferred AC field 1340 is a 2-bit field indicating the AC queue(value from 0 to 3) from which data should be sent by the node on the RUallocated to that node in the trigger frame.

The AC preference Level field 1330 is a bit indicating if the value ofthe Preferred AC field 1340 is meaningful or not. If the field 1340 isset to 1, then the node should take into account the preferred AC field1340 when selecting data at step 1130. If the field 1330 is set to 0,the node is allowed to send data from any AC queue, regardless of thepreferred AC field 1340 value.

The other fields of the trigger frame are defined in the 802.11axstandard.

The AP may also be in charge of broadcasting the EDCA parameters forboth EDCA mode and MU EDCA mode, as well as one or more initializingvalues to be used to initialize or reset the timers 2110 associated withthe traffic queues 210. The AP preferably performs the broadcastingusing a well-known beacon frame, dedicated to configure all the nodes inan 802.11 cell. Note the if the AP fails to broadcast the EDCAparameters, the nodes are configured to fall-back to by-default valuesas defined in the 802.11ax standard.

FIG. 14 a illustrates the structure of a standardized informationelement 1410 used to describe the parameters of the EDCA in a beaconframe.

Fields 1411, 1412, 1413, 1414 describes the parameters associated witheach traffic queue 210. For each traffic queue, a subfield 1415 includesthe EDCA parameters: AIFSN as a delay before starting to decrease theassociated backoff value, the ECWmin and ECWmax as the values of theminimum CW_(min) and maximum CW_(max) contention window and finally theTXOP limit as the maximum transmitting data time for an 802.11 device.

All the others fields of the information element are those described inthe 802.11 standard.

FIG. 14 b illustrates an exemplary structure of a dedicated informationelement 1420 to transmit the degraded EDCA parameter values according tothe invention, as well as a common initializing value for the timersHEMUEDCATimer[AC] of all the traffic queues. The dedicated informationelement 1420 may be included in a beacon frame sent by the AP.

The dedicated information element 1420 includes, for each AC queue, thedegraded EDCA parameters (1421, 1422, 1423, 1424) to be used by thenodes in the MU EDCA mode. It also includes a subfield 1425 specifyingthe common initializing value for the HEMUEDCATimers.

Each subfield 1421, 1422, 1423, 1424 includes the degraded AIFSN valuefor the corresponding traffic queue, as well as the degraded ECWminvalue and degraded ECWmax value (they can be the same as the legacy EDCAvalues).

In this embodiment, the predetermined degrading durations used toinitialize the timers HEMUEDCATimer[AC] associated with respectivetraffic queues AC are computed from the common initializing value 1425received from the AP and from an adjusting parameter specific to eachrespective traffic queue.

By using different adjusting parameters, different predetermineddegrading durations used to initialize the timers associated with tworespective traffic queues may be obtained.

In one embodiment, the common initializing value as provided by the APcan be multiplied by a constant value (adjusting parameter) based on thepriority of each traffic queue AC. For instance, the constant value canbe equal to 1 for AC_VO and AC_VI access categories and equal to 3 forAC_BE and AC_BG access categories.

FIG. 14 c illustrates another exemplary structure of a dedicatedinformation element 1430 to transmit the degraded EDCA parameter valuesaccording to the invention, as well as one initializing value for eachtimer HEMUEDCATimer[AC] implemented by the nodes. The dedicatedinformation element 1430 may be included in a beacon frame sent by theAP.

The dedicated information element 1430 includes, for each AC queue, aset of degraded parameters (1431, 1432, 1433, 1434) to be used by thenodes in the MU EDCA mode. It also includes a subfield 1425 specifyingthe common initializing value for the HEMUEDCATimers.

Each subfield 1431, 1432, 1433, 1434 includes the degraded AIFSN valuefor the corresponding traffic queue, as well as the degraded ECWminvalue and degraded ECWmax value (they can be the same as the legacy EDCAvalues), and finally the initializing value to be used for HEMUEDCATimerof the traffic queue concerned.

It means that the AP is in charge of computing and then of sending adedicated initializing value for each traffic queue. In this embodiment,the predetermined degrading durations used to initialize the timersHEMUEDCATimer[AC] associated with respective traffic queues are set torespective initializing values directly received from the AP.

To improve the QoS management, the initializing values computed by theAP are preferably based on the priority of each AC.

Although the present invention has been described hereinabove withreference to specific embodiments, the present invention is not limitedto the specific embodiments, and modifications will be apparent to askilled person in the art which lie within the scope of the presentinvention.

For instance, while the EDCA parameters and the degraded MU EDCAparameters are broadcasted in dedicated Information Elements of the samebeacon frame in the above explanations, variations may contemplatealternating between a beacon frame sending the EDCA parameters andanother beacon frame broadcasting the degraded MU EDCA parameters.

Many further modifications and variations will suggest themselves tothose versed in the art upon making reference to the foregoingillustrative embodiments, which are given by way of example only andwhich are not intended to limit the scope of the invention, that beingdetermined solely by the appended claims. In particular the differentfeatures from different embodiments may be interchanged, whereappropriate.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that different features are recited in mutuallydifferent dependent claims does not indicate that a combination of thesefeatures cannot be advantageously used.

1. A communication device, comprising: a transmitting unit configured totransmit data in an enhanced distributed channel access, EDCA,transmission opportunity, TXOP, using contention parameters; a receivingunit configured to receive, from an access point, a plurality of valuesfor MUEDCATimer which respectively correspond to a plurality of accesscategories, ACs, defined by IEEE802.11 series standards; and acontrolling unit configured to control the transmitting unit, in a casewhere data of a predetermined AC included in the plurality of ACs issuccessfully transmitted over a resource unit that is defined byIEEE802.11 series standards and is provided by the access point, so thatfirst parameters are used as the contention parameters for apredetermined duration that is based on a value, among the receivedplurality of values, which corresponds to the predetermined AC, and thecontention parameters are set back to second parameters different fromthe first parameters upon expiring the predetermined duration.
 2. Thecommunication device of claim 1, further comprising a plurality oftimers which respectively correspond to the plurality of ACs.
 3. Thecommunication device of claim 1, wherein the plurality of values forMUEDCATimer are included in a beacon frame transmitted from the accesspoint.
 4. The communication device of claim 1, wherein the resource unitis allocated by a trigger frame transmitted from the access point. 5.The communication device of claim 1, wherein the first parameters areincluded in a beacon frame transmitted from the access point.
 6. Thecommunication device of claim 1, wherein the contention parametersinclude at least CWmin which indicates lower boundary of a contentionwindow, CW, and CWmax which indicates higher boundary of the CW.
 7. Thecommunication device of claim 1, wherein the received plurality ofvalues include at least a first value corresponding to a first AC and asecond value corresponding to a second AC, and a duration based on thefirst value is different from a duration based on the second value. 8.The communication device of claim 1, further comprising a communicationunit for communicating a Request-To-Send (RTS) frame or a Clear-To-Send(CTS) frame.
 9. An access point, comprising: a transmitting unitconfigured to transmit, to a communication device, a plurality of valuesfor MUEDCATimer which respectively correspond to a plurality of accesscategories, ACs, defined by IEEE802.11 series standards; and a receivingunit configured to receive data from the communication device which, ina case where data of a predetermined AC included in the plurality of ACsis successfully transmitted over a resource unit that is defined byIEEE802.11 series standards and is provided by the access point, usesfirst parameters as contention parameters for a predetermined durationthat is based on a value, among the plurality of values, whichcorresponds to the predetermined AC, and sets the contention parametersback to second parameters different from the first parameters uponexpiring the predetermined duration.
 10. The access point of claim 9,wherein the plurality of values for MUEDCATimer are included in a beaconframe transmitted from the access point.
 11. The access point of claim9, wherein the resource unit is allocated by a trigger frame transmittedfrom the access point.
 12. The access point of claim 9, wherein thefirst parameters are included in a beacon frame transmitted from theaccess point.
 13. The access point of claim 9, wherein the contentionparameters include at least CWmin which indicates lower boundary of acontention window, CW, and CWmax which indicates higher boundary of theCW.
 14. The access point of claim 9, wherein the plurality of valuesinclude at least a first value corresponding to a first AC and a secondvalue corresponding to a second AC, and a duration based on the firstvalue is different from a duration base on the second value.
 15. Theaccess point of claim 9, further comprising a communication unit forcommunicating a Request-To-Send (RTS) frame or a Clear-To-Send (CTS)frame.
 16. A method for a communication device, comprising: transmittingdata in an enhanced distributed channel access, EDCA, transmissionopportunity, TXOP, using contention parameters; receiving, from anaccess point, a plurality of values for MUEDCATimer which respectivelycorrespond to a plurality of access categories, ACs, defined byIEEE802.11 series standards; and controlling the transmission, in a casewhere data of a predetermined AC included in the plurality of ACs issuccessfully transmitted over a resource unit that is defined byIEEE802.11 series standards and is provided by the access point, so thatfirst parameters are used as the contention parameters for apredetermined duration that is based on a value, among the receivedplurality of values, which corresponds to the predetermined AC, and thecontention parameters are set back to second parameters different fromthe first parameters upon expiring the predetermined duration.
 17. Amethod for an access point, comprising: transmitting, to a communicationdevice, a plurality of values for MUEDCATimer which respectivelycorrespond to a plurality of access categories, ACs, defined byIEEE802.11 series standards; and receiving data from the communicationdevice which, in a case where data of a predetermined AC included in theplurality of ACs is successfully transmitted over a resource unit thatis defined by IEEE802.11 series standards and is provided by the accesspoint, uses first parameters as contention parameters for apredetermined duration that is based on a value, among the plurality ofvalues, which corresponds to the predetermined AC, and sets thecontention parameters back to second parameters different from the firstparameters upon expiring the predetermined duration.
 18. Anon-transitory computer-readable medium storing a program which, whenexecuted by a microprocessor or computer system in a communicationdevice, causes the communication device to perform a method, the methodcomprising: transmitting data in an enhanced distributed channel access,EDCA, transmission opportunity, TXOP, using contention parameters;receiving, from an access point, a plurality of values for MUEDCATimerwhich respectively correspond to a plurality of access categories, ACs,defined by IEEE802.11 series standards; and controlling thetransmission, in a case where data of a predetermined AC included in theplurality of ACs is successfully transmitted over a resource unit thatis defined by IEEE802.11 series standards and is provided by the accesspoint, so that first parameters are used as the contention parametersfor a predetermined duration that is based on a value, among thereceived plurality of values, which corresponds to the predetermined AC,and the contention parameters are set back to second parametersdifferent from the first parameters upon expiring the predeterminedduration.
 19. A non-transitory computer-readable medium storing aprogram which, when executed by a microprocessor or computer system inan access point, causes the access point to perform a method, the methodcomprising: transmitting, to a communication device, a plurality ofvalues for MUEDCATimer which respectively correspond to a plurality ofaccess categories, ACs, defined by IEEE802.11 series standards; andreceiving data from the communication device which, in a case where dataof a predetermined AC included in the plurality of ACs is successfullytransmitted over a resource unit that is defined by IEEE802.11 seriesstandards and is provided by the access point, uses first parameters ascontention parameters for a predetermined duration that is based on avalue, among the plurality of values, which corresponds to thepredetermined AC, and sets the contention parameters back to secondparameters different from the first parameters upon expiring thepredetermined duration.